## Context
Fixes#22550. On app sync (`twenty dev`), a field backed by a
single-column unique constraint produces a **permanent, non-converging
`[isUnique] changed` field-metadata diff**: the change is reported, the
apply succeeds, and the identical change is reported again on the very
next sync.
## Root cause
Since the uniqueness-source-of-truth moved from a
`FieldMetadata.isUnique` column to `IndexMetadata` (@FelixMalfait's
#20846 / #20883), `field.isUnique` is a **derived** property. The two
sides of the app-sync diff derive it differently:
- **"from" side** (workspace cache,
`WorkspaceFlatFieldMetadataMapCacheService`) derives `isUnique` from
indexes via `computeUniqueFieldMetadataIdsFromIndexes`, which counted
**any** single-column `UNIQUE` index.
- **"to" side**
(`from-field-manifest-to-universal-flat-field-metadata.util.ts`) sets
`isUnique` from the field-level manifest flag (`fieldManifest.isUnique
?? false`).
For a field whose uniqueness is declared with `defineIndex({ isUnique:
true, fields: [oneField] })` (no field-level flag):
- "from" derives `true` (the custom unique index exists),
- "to" is `false` (no field-level flag),
so the diff emits a `fieldMetadata … [isUnique] changed` update forever.
The field-update runner drops `isUnique` before the SQL `UPDATE` (it has
no column), and the custom index persists, so the derived value never
changes — the loop cannot converge.
## Fix
Restrict the derivation in `computeUniqueFieldMetadataIdsFromIndexes` to
the field's **engine-owned backing constraint** — a `UNIQUE` index with
`isSystemSideEffect: true` — rather than any single-column unique index.
This makes `field.isUnique` mean the same thing on both sides:
| declaration | backing index (`isSystemSideEffect`) | "from" derived |
"to" flag | converges |
|---|---|---|---|---|
| field-level `isUnique: true` | side-effect handler generates it →
`true` | `true` | `true` | ✅ |
| `defineIndex({ isUnique: true, fields:[x] })` | custom index → `false`
| `false` | `false` | ✅ (index converges on its own) |
Standard objects and the create/update side-effect backing indexes are
all `isSystemSideEffect: true`
(`create-standard-index-flat-metadata.util.ts`,
`generate-deterministic-index-for-flat-field-metadata-or-throw.util.ts`),
so their fields keep `isUnique = true`. Only a user-declared custom
`defineIndex` unique index (`isSystemSideEffect: false`) is now excluded
— which is also what stops the create/update side-effect from generating
a **second, duplicate** backing index for a field the custom index
already covers (which would otherwise trip `DUPLICATE_UNIQUE_INDEX` on
first apply).
## Why this location (and not the manifest "to" side)
An earlier attempt derived `isUnique` on the manifest "to" side from the
built indexes. That breaks after #22295: `field.isUnique === true` is
the **trigger** for the `fieldUniqueBackingIndexOnCreate/Update`
side-effect handlers, so forcing it to derive from the compute-service
maps (which don't yet contain the not-yet-generated backing index) would
suppress the backing index for field-level unique fields. Narrowing the
shared "from" derivation keeps the side-effect trigger intact and makes
both sides symmetric in one place.
## For review — @FelixMalfait
This touches the uniqueness model you own in #20883 ("make IndexMetadata
the source of truth for uniqueness"), and interacts with the side-effect
engine from #22295. The semantic change is: **`field.isUnique` now
reflects only the field's backing constraint, not an arbitrary
user-declared single-column unique index.** A `defineIndex`-declared
single-column unique field now surfaces `isUnique: false` on the field
(the constraint is still enforced by the index). If instead you'd want
`defineIndex` single-column uniqueness to surface as `field.isUnique:
true`, the fix would need to live in the side-effect engine (dedupe the
backing index against the declared one) rather than the derivation —
happy to take it that direction. Flagging for your call before this
leaves draft.
## Related
- Issue #22550
- @FelixMalfait #20883, #20846 (IndexMetadata as source of truth for
uniqueness)
- #22295 (centralized side-effect engine — unique field backing index)
- #21383 (adjacent field-`isUnique` handling)
https://claude.ai/code/session_01T1Cqvt5tHS6tZ1FeQQWyRo
Marie
c8f7315c67